Grinding method

ABSTRACT

A precision flat surface is formed on a circular memory disk by rotating the disk on its axis and feeding a rotating annular grinding wheel axially into engagement with the disk under a substantially constant pressure. The grinding wheel is formed of a rigid foam material having abrasive particles dispersed therein and is supported for substantially friction-free axial movement.

United States Patent Inventors Jesse W. Elliott Dayton; Ralph R. Nevin, Pigua; Howard D. Wilkin, New Burlington, Ohio; William G. Huerth, Torrance, Calil. Appl. No. 812,778 Filed Apr. 2, 1969 Patented Aug. 31, 1971 Assignee H & H Industries, llnc.

Dayton, Ohio GRINDING METHOD 2 Claims, 10 Drawing Figs.

U.S. Cl 51/281 lR, 51/132, 51/165.9, 51/267 Int. Cl B24b l/Ot) Field of Search 51/281, 322,131,132,165,03,165.04,16S.045,267, 209,

[56] References Cited.

UNITED STATES PATENTS 504,386 9/1893 Johnston 51/132 1,040,470 10/1912 VanNostrand 5l/131 1,933,373 10/1933 Fraser 51/131 1,938,875 12/1933 Stratton 51/267 2,136,036 11/1938 Avery 51/281 2,168,596 8/1939 Hall 51/111 2,292,229 8/1942 Krueger 51/267 X 3,252,775 5/1966 Tocci-Guilbert 51/296 Primary Examiner-Lester M. Swingle Anorney-Marechal, Biebel, French & Bugg ABSTRACT: A precision flat surface is formed on a circular memory disk by rotating the disk on its axis and feeding a rotating annular grinding wheel axially into engagement with the disk under a substantially constant pressure. The grinding wheel is formed ofa rigid foam material having abrasive particles dispersed therein and is supported for substantially friction-free axial movement.

PATENTED AUB31 197i sum 1 or 3 IIVMEWTORS ELLIOTT, mavm HOWARD o. wluim a WILLIAM G. HUERTH @Ml @Np JESSE W. RALPH R.

PATENTEU #1231 m:

SHEET 2 0F 3 PATENTED AUBBI I97! SHEET 3 UP 3 FIG-9 FIG In the production of annular memory disks which are assembled in packs for use in computer systems, usually each disk is blanked from a sheet of aluminum or brass and is then finished on a lathe and then on a lapping machine to provide the disk with a uniform thickness and a precision surface finish on each face. It has been found that substantial heat is generated during both the rough lathe finishing operation and the lapping operation, and this heat causes warping of the disk so that it is extremely difficult to obtain e precise flatness which is desired.

Cooling fluids are commonly used during the turning and lapping operations for reducing the heat transfer into the disk, however, the problem of warping caused by a high concentration of heat within the disk has not been eliminated. While attempts have also been made to finish each disk by a grinding operation, it has been found difficult to produce disks of precisely uniform thickness. Moreover, as a result of the relatively soft material used for the disk. the grinding wheel quickly fills up with material removed from the disk, and abrasive particles from the grinding wheel are impregnated into the disk.

SUMMARY OF THE INVENTION The present invention is directed to an improved method for finishing a memory disk to produce a disk which is precisely flat, has a uniform thickness and a precision surface finish on each face. In accordance with one form of the method of the invention, a memory disk is finished by mounting it on a suction head having a horizontal axis of rotation and supported by a housing mounted on one end of a rectangular base formed of granite. A second housing is mounted on the other end of the base, and a air of parallel spaced guide rods extend horizontally between the housings. A carriage is supported for friction free movement by air bearings mounted on the guide rods and is moved on the rods by a hydraulic cylinder having a piston rod connected to the carriage.

A spindle is rotatably supported by the carriage on an axis extending in parallel laterally offset relation to the axis of the suction head and supports a grinding wheel including an annular body formed of a rigid polyurethane foam material and having abrasive particles dispersed therein. The grinding wheel is driven by a motor also mounted on the carriage and is fed axially by the hydraulic cylinder into engagement with the rotating memory disk. The pressure engagement of the grinding wheel against the disk is maintained substantially constant at a predetermined pressure selected in accordance with the rate of removal of material from the disk relative to the rate of removal of abrasive foam material from the grinding wheel. A liquid coolant is directed over the grinding wheel and the disk during the grinding operation to assure that the grinding wheel does not load up with the soft material removed from the disk and that abrasive particles removed from the grinding wheel are not embedded in the disk.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of grinding apparatus constructed in accordance with the invention;

FIG. 2 is a plan view of the apparatus shown in FIG. 1, with a portion of the cover broken away;

FIG. 3 is a fragmentary end view of the apparatus shown in FIGS. 1 and 2;

FIG. 4 is a fragmentary elevational view of the side opposite that shown in FIG. I, and showing generally the coolant recirculating system;

FIG. 5 is a fragmentary section taken generally on the line 5-5 of FIG. 3;

FIG. 6 is a fragmentary section of the carriage shown in FIG. 5;

FIG. 7 is an axial view of the rotary head shown in FIGS. 1 and 2, with a portion broken away;

FIG. 8 is a section taken generally on the line 8-6 of FIG. 7, and showing a memory disk in cross section;

FIG. 9 is a fragmentary section taken generally on the line the line 99 of FIG. 7; and

FIG. 10 is a view of the grinding wheel shown inFIGS. I and 2, with a portion broken away.

DESCRIPTION OF THE PREFERRED-EMBODIMENT The grinding apparatus or machine shown in FIG. l includes a rectangular blocklike base which is formed of granite and is supported by a cabinet 16 having a side door 17. A set of support stands or housings 20 and 22 are mounted on the ends of the base 15, and a pair of parallel spaced cylindrical guide rods 24 (FIG. 5) extend horizontally between the housings 20 and 22. A horizontally extending tubular spindle 25 is rotatably supported within the upper end portion of the housing 20 and is driven by a gear belt 26 connected to a variable speed transmission 28 driven by a motor 30. The spindle 25 may also be driven by a variable speed hydraulic motor.

A circular suction head is mounted on the inner end portion of the spindle 25 and includes a circular base 36 (FIG. 8) having a circumferential shoulder 37, an annular groove 38 and a recessed center cavity 39 connected by a passage 41 to the axially extending passage (not shown) within the spindle 25. A line 42 is connected to the spindle through a rotary joint 43 and is connected to a suction pump (not shown) enclosed within the cabinet 16. The head 35 further includes a circular plate 45 (FIG. 8) having a peripheral flange 46 which seats on the shoulder 37 of the base 36. A series of peripherally spaced screws 47 (FIG. 9 secured the plate 45 to the base 36, and an O-ring 48 forms an annular seal between the plate 45 and base 36.

An annular recess 50 (FIG. 8) is formed within the face of the plate 45 and is adapted to receive an unfinished annular memory disk D having a thickness somewhat greater than the depth of the cavity 50. An annular array of radial rows of axial holes 52 extend from the cavity 50 within the plate 45 and are connected by slightly larger corresponding passages 53 to radially extending grooves 54 formed] within the base 36 and extending from the cavity 39. Thus when a disk D is positioned within the cavity 50 and a partial vacuum is formed within the line 42, the disk is firmly retained on the head 35 by the differential pressure acting on the disk. To remove the disk D, the suction pump is reversed and air is pressurized within the holes 52.

Referring to FIG. 5, a carriage 60, is supported by the guide rods 24 for reciprocating movement between the housings 20 and 22 and includes four air bearings 62 (FIG. 6) which receive the guide rods 24. Each air bearing 62 includes a generally cylindrical bronze bushing 64 which is received within a corresponding cylindrical bore 66. An external circumferential cavity 67 is formed within the sleeve 64 and is connected by a series of peripherally spaced ports 68 to an internal circumferential groove 69 formed within an internal cylindrical bore 70 having a diameter slightly greater than he diameter of the guide rods 24.

Passages 72 and 73 extend within the carriage 60 to each bearing 62 and are connected to a source of pressurized air which is discharged through the ports 68 to form an air film between each bushing 64 and the corresponding guide rod 24. While the air bearings 62 are highly effective to eliminate substantially the frictional drag resisting the movement of the carriage 60 on the guide rods 24, other forms of substantially friction-free bearings may be employed, as for example, preloaded ball bearings retained within holes formed within a cylindrical cage.

Referring to FIG. 5, a hydraulic pressure cylinder 75 is positioned horizontally within the lower portion of the housing 20 and includes a piston rod 76 which is connected into the carriage 60 by a threaded fitting 77. Hydraulic fluid lines 78 and 79 connect the cylinder 75 to a hydraulic pump and reservoir system (not shown) which is enclosed within the cabinet 16. Pressure gauges 80 are mounted within the lines 78 and 79 to indicate the force exerted by the pressure cylinder 75 on the grooves 82, and a pair of inverted T-shaped grooves 84 extend laterally within the upper surface of the bracket 83. An electric motor 85 is mounted on the bracket 83 by bolts extending into the grooves 84 and is ventilated through a duct 86 which extends downwardly from the motor 85 and longitudinally adjacent the base 15. A bearing housing 88 is also mounted on the bracket 83 and supports a rotatable spindle 90 which is driven by the motor 85 through a belt drive 92 enclosed within a housing 93. The spindle 90 extends parallel to the spline 25 and is offset laterally within a horizontal plate as shown in FIG. 2. It is within the scope of the invention to employ a hydraulic motor for driving the spindle 90.

A grinding wheel 95 is mounted on the forward end portion of the spindle 90 and includes a circular aluminum base 96 (FIG. supported by a flange member 97. The base 96 and flange 97 are secured the spindle 95 by a nut 98 threaded onto the forward end of the spindle. The grinding wheel 95 also includes an annular body 100 having a flat annular surface 101 bonded to the aluminum base 96 and a flat annular working face 102.

The body 100 of the grinding wheel 95 is formed of a polymeric material consisting of a rigid porous foam having a high crush strength and abrasive particles dispersed therein. More specifically, the body 100 consists of a rigid polyu rethane abrasive foam which is constructed by mixing abrasive particles within one of the two liquid components of a polyurethane foam. The two liquid components are then mixed together and allowed to foam within a mold having the conv figuration of the body 100.

In one grinding wheel which produced highly satisfactory results, the two liquid polyurethane components and the abrasive particles were mixed in equal parts by volume. The liquid polyurethane components consisted of the 396 foam system produced by CPR-Upjohn Company, and the abrasive particles were silicon carbide. It is to be understood, however, that other abrasive particles such as aluminum oxide, boron carbide, serium oxide, tin oxide or diamond particles may also be used. The polyurethane components were foamed in place on the base 96 within an annular mold cavity and at a temperature of approximately 100 F. to produce a density of approximately l0 pounds per cubic foot. After the components set, the body 100 was dressed to form the annular flat radial working face 102.

Referring to FIG. 5, a threaded rod 105 extends through the housing 22 and has one end secured toe carriage 60. The rod 105 is slidably supported by a bearing 106 aligned with the piston rod 76 of the hydraulic cylinder 75. Adjustable nuts 108 are mounted on the rod 105 and are adapted to engage the bearing 106 when the carriage is moved to the left (FIG. 5) by the cylinder 75 and thereby provide a precisely adjustable limit or stop to the travel of the carriage 60. Another set of nuts M28 may be mounted on the rod 105 between the housing 22 and the carriage 60 if an adjustable precision stop is desired for limiting the travel of the carriage 60 to the right.

The hydraulic cylinder 75 is actuated by suitable solenoid valves (not shown) controlled by a limit switch 110 (FIG. 2) operated by the nuts 108 and a pair of switches 111 (FIG. I) mounted on the sides of the housing 22 and operated by corresponding fingeis 112 mounted on the carriage 60. Thus the travel of the carriage 60 and the grinding wheel 95 is determined by the setting of the nuts 108 and fingers 112.

Referring to FIG. 4, a manifold 120 is mounted on the bracket 83 and supports a set offlexible conduits 122 adjacent the grinding wheel 95. A line 121 connects the manifold 120 to a pump, reservoir and filtering system 125 which provides for recirculating a water base coolant or solution through the conduits 122 and over the grinding wheel face 102. A hood 130 is mounted on the cabinet 16 for covering the head 35 and grinding wheel and includes a door 132 which is supported for either sliding movement or for pivotable movement along its upper edge by a hinge 133. The hood 130 and door 132 are formed of a transparent plastic material to provide for viewing the grinding operation.

In operation, an annular memory disk D is positioned within the cavity 50 of the head 35, and suction is applied through the line 42 to the spindle 25, the cavity 39, channels 54 and the ports 52 so that the disk is positively retained within the cavity 50. The head 35 and disk D are rotated, and the hydraulic cylinder 75 is actuated so that the rotating grinding wheel 95 is fed axially until the face 102 engages the outer face of the disk D. A constant pressure, as for example, l5 p.s.i., is

maintained within the cylinder 75 so that a constant pressure H v v engagement is maintained between the face 102 of the grinding wheel 95 and the disk D for a predetermined time, as for example, 13 seconds. The carriage and grinding wheel then dwell for an approximately equal time to provide a cleanup operation, after which the carriage andgrinding wheel are retracted.

A water base coolant is directed over the grinding wheel and disk from the flexible lines 122, and the hood 130 directs the liquid coolant into a basin within the upper portion of the cabinet where the coolant is conducted back to the filtering and pump system 125. The door 132 within the hood 130 provides for convenient loading and unloading a disk D on the head 35, and the reversing of the suction pump connected to the line 42 provides for conveniently removing a disk from the head 35.

As mentioned above, the rotating grinding wheel 95 is held against the rotating disk D at a constant pressure for a predetermined time and then dwells to produce a precision microinch finish on the outer face of the disk. The grinding wheel 95 is then retracted by actuating the cylinder 75, the disk is reversed on the head 35, and the grinding operation is repeated for the opposite side of the disk D.

From the drawings and the above description, it becomes apparent that the finishing of a memory disk D in accordance with the invention provides desirable features and advantages. For example, the feeding of the friction-free supported grinding wheel 95 axially into pressure engagement with the rotating disk D and the maintaining of a constant pressure engagement between the grinding wheel and the disk while a fluid is directed over the grinding wheel and disk, result in producing a memory disk which is precisely flat and has a l-3 microinch finish. That is, the rigid abrasive foam composition of the body of the grinding wheel 95 and the liquid coolant cooperate to prevent the material of the aluminum disk from loading up the body 100 and the abrasive particles within the body 100 from being impregnated within the disk D. While the rate of removal of material from the grinding wheel body 100 is considerably greater than the rate of removal of material from the disk D, on the order of :1, the constant pressure engagement between the grinding wheel 95 and the disk D assures a uniform removal of material from the disk.

Another important advantage of the invention is that the finishing of the memory disl; D by the grinding wheel 95 is performed without any concentration of heat within the disk D so that the disk is prevented from warping. The low temperature grinding operation is primarily due to the porous foam composition of the grinding wheel body 100 and the cooperation of the liquid coolant directed over the grinding wheel and disk.

Another important feature provided by the apparatus of the invention is the friction-free support of the carriage 60. That is, the air bearings 62 substantially eliminate the frictional drag which opposes the force exerted by the cylinder 75 during the slow movement of the carriage 60 and grinding wheel 95 during the grinding operation, and thereby assure that the pressure engagement of the grinding wheel 95 against the disk D remains substantially constant.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may bemade in either without departing from the scope of the invention. For example, a second motor driven grinding wheel 95 may also be supported by the carriage 60 and be shiftable'into position to provide an initial rough finishing operation, or a plurality of grinding wheels 95 may be employed in radially spaced elation for finishing a larger diameter disk D.

We claim:

1. An improved method of forming a precision flat surface on a circular disk, comprising the steps of rotating the disk on its axis at a predetermined speed, forming a grinding wheel a rigid inflexible, foam material with abrasive particles dispersed therein, rotating the grinding wheel on an axis extending parallel to the axis of the disk and in offset relation, supporting the rotating said grinding wheel for substantially friction-free axial movement toward the disk, moving the rotating said grinding wheel axially into pressure engagement with the rotating disk, and holding said pressure engagement at a predetermined constant pressure for a predetermined time according to the rate of removal of material from the disk and the breakdown of particles from the grinding wheel.

2. A method as defined in claim 1 including the step of reducing said pressure after said predetermined time while maintaining said pressure engagement to complete the finish ing of the disk surface to a predetermined microfinish.

222g? UNITED STATES PAJENT OFFICE CERTEFICATE OF CORRECTION Patent No. 3,601,932 Dated August 31, 1971 Jesse W. Elliott, Ralph R. Nevin, Howard D. Wilkin @161 William G. nuertn It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor(s) Column 1, line 14, "e" should be --the. 1

Column 1, line 38, "air" should be -pair-.

Column 2, line 6, there is an extra "the line".

Column 3, line 7, "he" should be -the-.

Column 3, line 26, "to" is omitted.

Column 3, line 56 "ton" should be -to the.

Column 4, line 58, "110:1" should be -l0:l.

Column 6, line 1, after "wheel" the word a" should be -of--.

Column 6, line 2, "nonresilient" has been omitted, after inflexible,

Signed and sealed this 18th day of April 1972.

Attcst:

JED IARD PLPLETCIIAR, Jli. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. An improved method of forming a precision flat surface on a circular disk, comprising the steps of rotating the disk on its axis at a predetermined speed, forming a grinding wheel a rigid inflexible, foam material with abrasive particles dispersed therein, rotating the grinding wheel on an axis extending parallel to the axis of the disk and in offset relation, supporting the rotating said grinding wheel for substantially friction-free axial movement toward the disk, moving the rotating said grinding wheel axially into pressure engagement with the rotating disk, and holding said pressure engagement at a predetermined constant pressure for a predetermined time according to the rate of removal of material from the disk and the breakdown of particles from the grinding wheel.
 2. A method as defined in claim 1 including the step of reducing said pressure after said predetermined time while maintaining said pressure engagement to complete the finishing of the disk surface to a predetermined microfinish. 